Dynamics of SARS-CoV-2 Antibody Response in a Longitudinal Cohort of Healthcare Workers from India

Introduction: Coronavirus Disease 2019 (COVID-19) pandemic has affected healthcare systems worldwide. Healthcare Workers (HCWs) form one of the most at-risk population groups for acquiring infection. Trend analysis of anti Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) antibody titres in vaccination naïve HCWs will give an insight into the role of natural protective immunity against reinfection.

Aim: To understand the dynamics of anti SARS-CoV-2 antibody response and its protective role against reinfection in a cohort of HCWs.

Materials and Methods: This observational longitudinal cohort study was conducted in a tertiary care hospital in Gurugram, Haryana, North India from June to December 2020. The study was approved by the Institutional Ethics Committee. Serum specimens from 230 HCWs were tested for anti-spike protein Immunogloublin G (IgG) antibodies by chemiluminescence immunoassay. The HCWs with positive antibody status and previous Polymerase Chain Reaction (PCR) confirmed infection (n=47) were followed-up over 180 days for serial antibody titres at four visits, each at a gap of 30-45 days. Participants were classified into asymptomatic (n=18), mild (n=17) and moderate (n=12) disease categories based on severity of previous COVID-19
illness. SPSS version 22.0 was used for statistical analysis. Intergroup comparison of means was done using Kruskal-Wallis test and Chi-square test. The p<0.05 was considered statistically significant.

Results: Positivity rate for anti SARS-CoV-2 IgG antibodies was 25.7%. Seroconversion rate was 90.74% in HCWs with history of previous Real Time-Polymerase Chain Reaction (RT-PCR) confirmed COVID-19 infection. Incidence of infection in seronegative group (n=171) was 12.96 per 10,000 person days while in seropositive group, it was 1.29 per 10,000 person days. Risk ratio for infection (baseline seronegative vs baseline seropositive) was determined to be 8.12 [95% Confidence Interval (CI) 1.068-61.755]. Incidence of PCR confirmed SARS-CoV-2 reinfection was inversely associated with antibody titres (p=0.018). Antibody response trend showed a peak in mean titres in the 46-90 days period followed by steep decline till 135 days and a gradual waning till 180 days.

Conclusion: Significant postinfection immunity is offered by even low to moderate amounts of antibodies and this occurs regardless of whether a seropositive HCW had previous asymptomatic or symptomatic infection. These findings have significant implications in establishing the protective role of anti-spike protein antibodies against subsequent infection